(Adds farmers protest at PM's temporary office)
By Amy Sawitta Lefevre
BANGKOK, Feb 17 (Reuters) - Hundreds of unpaid Thai rice farmers swarmed around the temporary office of Prime Minister Yingluck Shinawatra on Monday, threatening to storm the building if the beleaguered premier did not come out and speak to them.
The escalation of the protest by farmers, who have not been paid for crops sold to the government under a state rice-buying scheme that helped sweep Yingluck's Puea Thai Party to power, came as thousands of demonstrators seeking to unseat the prime minister surrounded the government's headquarters.
Live television pictures showed farmers climbing over barbed wire fences and barriers at the Defence Ministry compound in north Bangkok where Yingluck has set up temporary offices. They pushed back a line of riot police, who retreated from confrontation, but did not enter the building.
"The prime minister is well-off but we are not. How are we going to feed our children? I want her to think about us," said one protesting farmer.
"Farmers are tough people, they wouldn't normally speak out but they are at the end of their tether," she added.
The farmers have mostly kept apart from a broader anti-government protest movement, about 10,000 of whose members surrounded the prime minister's main Government House offices in central Bangkok early on Monday.
Those protesters view Yingluck as a proxy for her elder brother, Thaksin Shinawatra, a self-exiled former prime minister who clashed with the establishment before he was overthrown by the army in 2006.
"We will use quick-dry cement to close the gates of Government House so that the cabinet cannot go in to work," Nittitorn Lamrue, leader of the Network of Students and People for Thailand's Reform, a group aligned with the main protest group, told reporters.
The disturbances came as gross domestic product (GDP) data showed growth slowed sharply in the final quarter of 2013, as the political paralysis caused by months of unrest and a disrupted election began to take its toll on Southeast Asia's second-largest economy.
Protesters moved concrete barriers to block entrances of Government House and poured cement over the barriers in what they said was a "symbolic gesture" to show the building was closed. Yingluck has been forced to work from the temporary offices since January.
NOT USING FORCE
"There are enough soldiers and police inside Government House to protect the building and the grounds," National Security Council Chief Paradorn Pattanathabutr told Reuters. "The protesters said they will not come inside so we aren't expecting a confrontation."
Bluesky TV, the protest movement's television channel, showed demonstrators spilling into the grounds of the nearby Ministry of Education. Protest leaders asked officials working there to leave the ministry, or join their movement.
Broadly, the political crisis pits the Bangkok middle class and royalist establishment against supporters of Yingluck and her billionaire brother Thaksin, who has lived abroad since 2008 to avoid a jail sentence for a graft conviction he says was political motivated.
Demonstrators accuse Thaksin of nepotism and corruption and say he used taxpayers' money for generous subsidies and easy loans that have bought him loyalty from millions of working-class voters in the north and northeast.
An election on Feb. 2 failed to heal the deepening crisis. Protesters disrupted polls in a fifth of constituencies, a result that left parliament without a quorum to approve a new government leaving Thailand in political limbo under a caretaker administration with limited powers.
Hundreds of riot police began an operation on Friday to reclaim protest sites and reopen roads and state offices, some of which have been blocked for more than three months.
Labour minister Chalerm Yoobamrung, who is in charge of the security operation, said police would press ahead with a plan to reclaim protest sites near government buildings.
The protesters, led by firebrand former deputy premier Suthep Thaugsuban, have vowed to remain on the streets until they topple Yingluck's government and usher in political reforms before an election.
Security forces put up little resistance when protesters move to occupy ministries and key intersections over the past few months.
The government, haunted by memories of a bloody 2010 crackdown by a previous administration that killed dozens of pro-Thaksin "red shirt" activists, has largely tried to avoid confrontation.
Despite that cautious approach, 11 people have been killed and hundreds hurt in sporadic violence between protesters, security forces and government supporters.
The protest movement has seen numbers dwindle but has experienced a second wind by trying to align itself with the protesting rice farmers.
The country's anti-corruption agency is investigating allegations that Yingluck, who is head of the national rice committee, was negligent in her role overseeing the programme. (Additional reporting by Panarat Thepgumpanat and Athit Perawongmetha; Editing by Alex Richardson and Robert Birsel)